1. Field of the Invention
The present invention relates to a method for producing an aluminum drum adapted for use in electronic copying machines, laser beam printers and magnetic roller sleeves, and more particularly to an aluminum drum having a highly smooth surface. The term "aluminum" as herein employed includes aluminum alloys.
2. Description of the Prior Art
An electronic copy machine and a laser beam printer use aluminum drums for exposing a film or the like to light thereon. In this case the drum must be as smooth as not larger than 0.8 to 1 .mu.m Rmax. To produce aluminum drums having such highly smooth surfaces there is one proposal; according to it an aluminum pipe is first produced by extrusion, and then the pipe is drawn, during which if necessary correction is made on the dimensional precision and profile.
The pipe is drawn through a special die unit which consists of a die and a plug, wherein the die includes a die bore adapted to allow an aluminum pipe to pass through. The die bore diverges at a certain angle outward, and the stress to which the pipe is subjected during drawing depends on the angle of the die bore. It has been taught that to minimize the stress the angle should be adjusted to 16.degree. to 20.degree..
However the surfacial smoothness of the pipe does not reach the degree that the drum can be used as an exposing drum in the electronic copying machines. Therefore it becomes necessary to polish the surface of the pipe so as to reach the required degree of smoothness.
In this way the known process requires two steps, thereby leading to the increased production cost. In general the industry of electronic copying machines is very competitive with so many manufacturers, and in order to win the competition the reduced price as well as the quality of the machines are great concerns for them.